In steam dispersion, either pressurized steam from a boiler or un-pressurized steam from an atmospheric steam generator is often used to humidify spaces within buildings. The steam is piped to a steam dispersion device which distributes the steam into an air duct, air handling unit (AHU) or open space. According to a conventional system, the steam dispersion device may consist of a manifold (referred to as a header) to which may be attached a row of stainless steel tubes.
Steam is normally discharged from a steam source as dry gas or vapor. When steam enters a steam dispersion system and mixes with cooler duct air, condensation takes place in the form of water particles. Within a certain distance, the water particles become absorbed by the air stream within the duct. The distance wherein water particles are completely absorbed is called absorption distance. Alternatively, there is the distance wherein water particles or droplets no longer form on duct equipment (except high efficiency air filters, for example). This is known as the non-wetting distance. Absorption distance is typically longer than non-wetting distance. Before the water particles are absorbed into the air within the non-wetting distance and ultimately the absorption distance, the water particles collect on duct equipment. The collection of water particles may adversely affect the life of such equipment. Thus, a short non-wetting or absorption distance is desirable.
To achieve a short non-wetting or absorption distance, steam dispersion systems may utilize multiple, closely spaced, stainless steel, dispersion tubes. The number of tubes and their space are based on needed non-wetting or absorption distance. The dispersion tubes can get very hot (e.g., around 212° F. on outer surface). When a large number of tubes get hot, they heat the surrounding duct air. This ultimately reduces the effect of the cooling and humidification process, thus resulting in wasted energy. Moreover, cool air (e.g. at 50-70° F.) that flows around the hot dispersion tubes causes a portion of the steam within the dispersion tubes to condense and form condensate. The condensate is often drained out of the steam dispersion system, thus wasting water. Stainless steel tubes are conventionally perforated with holes or provided with nozzles to prevent condensate from exiting (spitting). Moreover, perforated tubes may be better at evenly distributing steam to promote rapid absorption into the air.
However, even perforating stainless steel tubes cannot combat many of the disadvantages associated with a typical steam dispersion device. Cool air flowing across the hot dispersion tubes still causes some steam to condense within the dispersion tubes, which is drained out of the device and exits the AHU, wasting water. The dispersion system still heats the air, increasing cooling costs. Static air pressure drop across the dispersion device is always a problem, increasing fan horsepower year round, even when the dispersion device is not used. Rigid stainless steel tubes, headers, and frames may be costly from both a material and shipping perspective. Insulation may be added to the dispersion tubes to reduce condensate and heat gain, however, leading to increased costs and static air pressure drop.
The contradiction that is always present in steam dispersion systems is that short absorption distances require more dispersion tubes, thus creating more condensate, heat gain, and static air pressure drop and designing a system that reduces condensate, heat gain, and static air pressure drop requires the use of fewer tubes, which, however, lead to longer absorption distances.
What is needed in the art is a steam dispersion device that will simultaneously provide short absorption distances, reduced condensate, reduced heat gain and static air pressure drop while achieving a reduction in material, storage, shipping, handling, and installation costs.